Diabetes mellitus is a type of metabolic disease that causes an insufficient secretionary amount of insulin or a dysfunction thereof, and is characterized by hyperglycemia (having a high blood glucose level). Hyperglycemia causes several symptoms and signs, and glucose to be excreted in urine. In addition, as time passes, vascular disorders and dysfunctions in nerves, kidneys, retinas, and the like are caused, which results in death.
There are two types of diabetes: type 1 and type 2. Type 1 diabetes is called “juvenile diabetes” and occurs when no insulin is produced. Type 2 diabetes is caused by a relative lack of insulin and is characterized by insulin resistance (cells do not process glucose efficiently due to a degradation in a function of insulin that lowers a blood glucose level). Type 2 diabetes is thought to mainly result from environmental factors such as a high-calorie, a high-fat, and a high-protein diet present in a westernized diet, lack of exercise, and stress. Besides the environmental factors, diabetes may be caused by a defect of a specific gene, pancreatic surgery, infection, or drugs.
Recently, due to a westernized diet, stress, lack of exercise, and the like, chronic and life-style related adult diseases such as arteriosclerosis, hypertension, and diabetes have been increasing. In particular, in Korea, the prevalence of diabetes is consistently increasing: less than 1% of the population in the 1970s, about 3% in the late 1980s, and 5 to 8% in the 1990s. Accordingly, up to now, various types of therapeutic agents for diabetes have been developed but a satisfactory treating method or medicine has not been developed yet.
The insulin resistance, which is a feature of type 2 diabetes, is caused by a defect of insulin secretion itself and decrease in insulin signaling. Accordingly, recently, a method of treating diabetes by increasing insulin signaling has been newly proposed. For this purpose, a method of suppressing expression of proteins such as PTP1B (protein tyrosine phosphatase 1B) that inhibits a function of an insulin receptor is under development. However, in type 2 diabetes, a problem in insulin signaling is generally caused by degradation of a function (a decrease in the amount of protein and tyrosine phosphorylation of IRS-1) of IRS-1 (insulin receptor substrate-1) rather than a functional degradation of the insulin receptor. Accordingly, a protein capable of regulating the function of IRS-1 is important since it can be a target for treating diabetes and complications associated with diabetes. However, a protein that directly influences as PTPase (protein tyrosine phosphate) of IRS-1 in association with diabetes has not been reported yet. A case in which such PTPase regulates both an amount of protein and phosphorylation of IRS-1 has not been reported yet.
In this way, a protein capable of regulating a decrease in the amount of protein and phosphorylation of IRS-1 can be an effective target of a therapeutic agent for diabetes or complications of diabetes. Therefore, discovering such a target protein and development of a therapeutic agent for diabetes or complications of diabetes using the same are necessary.